This invention relates to high transverse dipole moment aryl compounds and their use in liquid crystal compositions and liquid crystal devices wherein a high transverse dipole moment is required.
U.S. Pat. No. 4,784,793 discloses terpenoid derivatives for incorporation into ferroelectric liquid crystal mixtures, such terpenoid derivatives including aromatic esters of terpenoid alcohols in which the aromatic group includes two or three phenyl groups which may be biphenyl or terphenyl groups. The possibility of providing lateral substituents on one or more of these phenyl groups is disclosed with the object of fixing the orientation of such groups to add to the total lateral dipole moment of the molecule. The use of methyl, methoxy, trifluoromethyl, cyano, halogeno and acetyl groups as such lateral substituents is mentioned. U.S. Pat. No. 4,952,337 discloses similar types of compound to those disclosed in above-mentioned U.S. Pat. No. 4,784,793.
U.S. Pat. No. 4,852,977 discloses compounds which may be used as a host or dopant in ferroelectric chiral smectic liquid crystal mixtures, the compounds being derivatives of an xcex1-hydroxycarboxylic acid containing a chiral unit in which the asymmetric carbon atom is linked to a hydrogen atom, a phenyl or phenyl alkyl group where the phenyl ring may be substituted with one or more alkyl, alkoxy, halogen or cyano groups, and two other moieties linked to the asymmetric carbon atom by carbonyloxy groups. The compound may include bi- or ter-phenyl groups which may or may not be substituted by one or more fluorine atoms to assist in sterically hindering rotation of the chiral centre relative to the core of the molecule.
It is an object of the present invention to provide a compound having an improved transverse dipole moment.
According to a first aspect of the present invention, there is provided a fluorinated aryl compound having the general formula [1]: 
wherein
A, B and C are independently selected from conjugated cyclic moieties including heterorings and fused rings;
the fluoro substituent on ring A is at the ortho position relative to the attached end chain;
R1=straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C12)alkyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C12)alkoxy, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C11)alkoxycarbonyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C11)alkylcarbonyloxy, cyano, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C12)alkenyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C12)alkenyloxy, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C11)alkenyloxycarbonyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C11)alkenylcarbonyloxy, or R6xe2x80x94(CHFxe2x80x94CH2)axe2x80x94(CF2xe2x80x94CH2)bxe2x80x94CF2xe2x80x94(CH2)cxe2x80x94;
R2=H or F;
R3=straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C12)alkyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C12)alkoxy, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C11)alkoxycarbonyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C11)alkylcarbonyloxy, cyano, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C12)alkenyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C12)alkenyloxy, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C11)alkenyloxycarbonyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C11)alkenylcarbonyloxy;
R4=H or F;
R5=H or F;
R6=straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C12)alkyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C12)alkoxy, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C11)alkoxycarbonyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C1-C11)alkylcarbonyloxy, cyano, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C12)alkenyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C12)alkenyloxy, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C11i)alkenyloxycarbonyl, straight or branched, fluoro- and/or cyano-substituted or unsubstituted (C2-C11)alkenylcarbonyloxy;
a=0, 1 or 2;
b=0, 1 or 2;
c=0 or 1;
s=0 or 1;
t=1, 2 or 3;
u=1, 2 or 3;
v=0 or 1;
x=0 or 1;
y=0, 1 or 2; and
z=0, 1 or 2;
More specifically, the compound of a fluorinated aryl compound may have the general formula [1a]: 
wherein u=1, 2 or 3, v=0 or 1, x=0, 1 or 2; y=0, 1 or 2; z=0, 1 or 2; A and B are independently selected from conjugated cyclic moieties including heterorings and fused rings; the fluoro substituent on ring A is at the ortho position relative to the chain containing R3; R1=(C1-C12)alkyl, (C1-C12)alkoxy, (C1-C11)alkoxycarbonyl, (C1-C11)alkylcarbonyloxy, or cyano; R2=H or F, R3=(C1-C11)alkyl, (C1-C11)alkoxy, (C1-C10)alkoxycarbonyl or (C1-C10)alkyl carbonyloxy; and R4=H or F.
A, B and C are preferably aryl moieties, and are more preferably independently selected from phenyl, pyridinyl and pyrimidinyl.
Examples of compounds within the scope of the present invention are in accordance with the general formulae [2] to [12] below, wherein R is (C1-C10)alkyl and Rxe2x80x2 is (C1-C12)alkyl: 
wherein a is 0 or 1, b is 0 or 1 and v is 0 or 1
wherein a is 0 or 1, b is 0 or 1 and v is 0 or 1 
wherein a is 0 or 1, b is 0 or 1 and v is 0 or 1
wherein a is 0 or 1, b is 0 or 1 and v is 0 or 1
wherein a is 0 or 1, b is 0 or 1 and v is 0 or 1 
where a is 0 or 1, v is 0 or 1 and R2 and R4 are as defined above 
where a is 0 or 1, v is 0 or 1 and R2 and R4 are as defined above
In all of the above examples v=0 or 1, but in the case of terphenyl compounds, those compounds where v=0, i.e. where the side chain CF2 group is at the alpha position relative to the adjacent ring, may be preferred.
Compounds of the general formulae [11] and [12] above are examples of nematics having a high positive dielectric biaxiality, i.e. nematics in which the liquid crystal molecules align parallel to the direction of an applied electrical field.
Compounds within the scope of the present invention also include compounds of the general formula: 
where R1 is (C1-C12)alkyl or (C1-C12)alkoxy and R3 is (C1-C12)alkyl
A particular example of a compound of the general formula [1] above is the compound having the formula [13] below: 
The measured dipole moment (following the procedure of E. P. Raynes (1984) Mol. Cryst. Liq. Cryst. Lett., v1 p 69) of compound [13] is 16.48xc3x9710xe2x88x9230 Cm. Based on dipole moment calculations for a compound containing the moieties, Rxe2x80x2O-phenyl-phenyl-3,4-difluorophenyl- and RCF2CH2xe2x80x94, the measured dipole moment for compound [13] is closest to the value predicted for a substantially parallel arrangement of the dipoles of these two moieties rather than an anti-parallel or random orientation. The estimated change of the nematic xcex94xcex5 and SmC(*) xcex4xe2x8axa5≈xcexcxe2x8axa52, where xcex5xe2x8axa5 is the dipole moment perpendicular to the long axis of the molecule. Since the measured dipole moment of a similar compound having no RCF2CH2xe2x80x94 moiety was 10.9xc3x9710xe2x88x9230 Cm, the compound [13] may represent an improvement of a factor of greater than 2 over the latter compound.
It is also considered that any tendency for the CF2 fluorines to align parallel with the fluorine on the adjacent phenyl group of the core may enable suitable liquid crystal phases to be achieved with compounds having shorter cores than has heretofore been considered possible.
The difluoro side chain moiety in the compounds according to the present invention can be introduced using the following reaction scheme which is given, purely by way of example, in connection with a compound of the formula (1) wherein z and y are both 0. 
According to a second aspect of the present invention, there is provided a liquid crystal composition containing a compound according to said first aspect of the present invention.
The nature of compound of the invention chosen for use in the liquid crystal composition depends upon the nature of the device in which the composition is to be used, as will be apparent hereinafter.
According to a third aspect of the present invention, there is provided an electro-optical liquid crystal device including a liquid crystal cell have a layer of a liquid crystal composition according to said second aspect of the present invention, and means for applying an electrical field across said layer.
The present invention is particularly applicable to devices having any of the following:
(a) a nematic liquid crystal layer arranged to work in ECB or VAN mode, in which a large negative dielectric anisotropy xcex94xcex5 is required for low voltage switching of the liquid crystal molecules into the plane of the cell,
(b) a ferroelectric liquid crystal (FLC) layer using AC field stabilisation and/or xcfx84Vmin (or reverse mode) operation, in which a large positive dielectric anisotropy is required,
(c) highly multiplexed nematic layers having SmC components with high negative dielectric anisotropy and/or high positive dielectric biaxiality for a steep electro-optical response and therefore a high level of multiplexibility, and
(d) a nematic liquid crystal layer arranged to exhibit a large flexoelectric effect.
The present invention is also applicable to other devices, e.g. those containing antiferroelectric smectic materials or N* materials.
The compound of the formula [13], namely 
was prepared according to the following reaction scheme: 
Reagents
a . . . (i) n-butyllithium, xe2x88x9270xc2x0 C., THF; (ii) 1,2-epoxyoctane; (iii) boron trifluoride etherate
b . . . chromic acid, ether
c . . . 1,2-ethanedithiol, boron trifluoride-acetic acid
d . . . 70% hydrogen fluoride-pyridine, dichloromethane, 1,3-dibromo-5,5-dimethylhydantoin
e . . . (i) n-butyllithium, xe2x88x9270xc2x0 C., THF; (ii) trimethyl borate; (iii) 10% HClaq 
f . . . 1-bromo-4-iodobenzene, 1,2-dimethoxyethane, 2 M Na2CO3, Pd(PPh3)4 
g . . . 1,2-dimethoxyethane, 2 M Na2CO3, Pd(PPh3)4 
Melting points and liquid crystal transition temperatures were measured using a Mettler FP5 hot-stage and control unit in conjunction with an Olympus BH2 polarising microscope. These were confirmed by differential scanning calorimetry (DSC) carried out on a Perkin Elmer DSC 7 with TAC 7/PC instrument interface and controlled cooling accessory. Heating and cooling rates were at 10xc2x0 C. minxe2x88x921. A nitrogen atmosphere was maintained in the furnace. The reference sample was gold and the calibration sample was indium. Melting points for liquid crystalline compounds are those of the DSC onset value (1st heating cycle). Analytical thin-layer chromatography (TLC) was performed on Kieselgel silica 60 F254, backed onto aluminium sheets, and spots were visualised with UV light and iodine. The progress of reactions was often monitored using a Chrompak 9001 capillary gas chromatograph fitted with a CP-SIL 5 CB 10 mxc3x970.25 mm, 0.12 xcexcm column (Cat. No. 7700) (N2 carrier) and a flame ionisation detector. Purity of compounds was checked by high performance liquid chromatography (HPLC) on a Lichrocart 125-4 Superspher RP18 column connected to a Merck-Hitachi L-4000 UV detector, L 6200A pump, D-6000 interface and D-6000 HPLC manager eluting with chloroform/acetonitrile. Infrared (IR) spectra were obtained using a Perkin Elmer 983G spectrometer (s=strong, w=weak) as thin films or potassium bromide discs. 1H NMR spectra were recorded on a JEOL JMN GX270 FT spectrometer (270 MHz) or a JEOL 400 MHz machine in deuteriochloroform. Chemical shifts are reported in ppm from an internal standard of TMS. Selected data are reported as follows: chemical shift, multiplicity (s=singlet, d=doublet, t=triplet, q=quartet, m=multiplet, br=broad), coupling constant (hertz) and assignment. Mass spectra were recorded on a Finnigan MAT 1020 GC/MS spectrometer, M+ represents the molecular ion. Flash chromatography was carried out using Sorbsil C60 (40-60 xcexcm) grade silica. THF was freshly distilled from potassium. Light petroleum refers to the fraction (b.p. 40-60xc2x0 C.) unless otherwise stated. Organic solvent extractions were dried over magnesium sulphate unless otherwise stated.
Step 1(a)xe2x80x94Preparation of 1-(2,3-Difluorophenyl)-octan-2-ol
To a stirred solution of 1,2-difluorobenzene 1 (20.0 g, 0.175 mol) in dry THF (300 ml) was added dropwise a solution of 2.5 M n-butyllithium (68 ml, 0.17 mol) at xe2x88x9270xc2x0 C. under dry nitrogen. The addition rate was such that the temperature did not rise above xe2x88x9260xc2x0 C. After the addition was completed the reaction was stirred at xe2x88x9270xc2x0 C. for 2 h. 1,2-Epoxyoctane (21.6 g, 0.169 mol) was added slowly followed by the dropwise addition of boron trifluoride etherate (21 ml, 0.17 mol). The mixture was allowed to warm to room temperature overnight, acidified with 10% hydrochloric acid and extracted into ether. The combined extracts were washed with sat. aqueous sodium chloride and evaporated to give a viscous liquid. Kugelrohr distillation (130xc2x0 C., 0.15 mm Hg) yielded 1-(2,3-difluorophenyl)-octan-2-ol (30.8 g, 74%) which crystallised on standing; Vmax 3370 br (OH), 2950, 2920, 2850, 1620, 1590, 1480 s, 1280, 1205, 1070 br, 825, 775, and 730 cmxe2x88x921, xcex4H 0.88 (3 H, t, Me), 1.23-1.40 (10H, m, CH2), 1.40-1.58 (4 H, m overlapping br s, CH2CHOH and OH), 2.72 (1 H, ddd, J16, 8 and 2 Hz, ArCH2), 2.91 (1 H, ddd, J16, 6, and 2 Hz, ArCH2), 3.86 (1 H, m, CHOH), and 6.94-7.09 (3 H, m, ArH); m/z 242 (M+), 225, 198, 157, 139, 128, and 97.
Step 1(b)xe2x80x94Preparation of 1-(2,3-Difluorophenyl)-octan-2-one
A solution of chromic acid1 (31.6 ml, 21.0 mmol) was added dropwise to a rapidly stirred solution of the octan-2-ol produced in step 1(a) in ether (100 ml) cooled in a water bath. The mixture was stirred for 2 h; water was added and the mixture was extracted with ether (twice). The combined extracts were washed with water, 1 M aqueous sodium hydroxide, sat. sodium bicarbonate solution and dried and evaporated. Kugelrohr distillation (125xc2x0 C., 0.02 mm Hg) gave the required ketone as a clear liquid (11.9 g, 80%); vmax 2950, 2920, 2850, 1710 s (CO), 1620, 1590, 1480 s, 1410, 1275, 1205, 1060, 820, and 775 cmxe2x88x921, xcex4H 0.90 (3 H, t, Me), 1.14-1.37 (6 H, m, CH2), 1.60 (2 H, quint CH2CH2CO), 2.51 (2 H, t, CH2CH2CO), 3.75 (2 H, s, ArCH2), and 6.87-7.13 (3 H, m, ArH); m/z 240 (M+), 183, 171, 151, 141, 133, 127, and 113.
[1 B. S. Furniss, A. J. Hannaford, V. Rogers, P. W. G. Smith and A. R. Tatchell in Vogel""s Textbook of Practical Organic Chemistry, 4th Ed., Longman, N.Y., 1978, p 426.]
Step 1(c)xe2x80x94Preparation of 2-(2,3-Difluorobenzyl)-2-hexyl-[1,3]dithiolane
Boron trifluoride-acetic acid (9.2 g, 6.8 mmol) was added under an atmosphere of nitrogen to a rapidly stirred mixture of ethane-1,2-dithiol (9.2 g, 8.2 mmol) and the ketone produced in step 1(b) (11.5 g, 48.7 mmol). After stirring at ambient temperature for 2 h water was added and the mixture was extracted with ether (twice). The combined extracts were washed with 2 M aqueous sodium hydroxide, sat. sodium bicarbonate solution and dried. The solvent was removed in vacuo and Kugelrohr distillation (140xc2x0 C., 0.5 mm Hg) gave the required dithiolane, a pale yellow liquid 4 (14.7 g, 95%); vmax 2950, 2920, 2850, 1620, 1590, 1480 s, 1285, 1260, 1220, 1200, 1065, 1005, 990, 830, 785, and 740 cmxe2x88x921, xcex4H 0.89 (3 H, t, Me), 1.24-1.38 (6 H, m, CH2), 1.63 (2 H, m, CH2CH2C), 1.92 (2 H, m, CH2CH2C), 3.02-3.13 (2 H, m, CH2), 3.16-3.25 (2 H, m, CH2),3.26 (2 H, d, J1.5 Hz, CH2Ar), 6.95-7.12 (2-H, m, ArH), and 7.22-7.30 (2 H, m, ArH); m/z 316 (M+), 231, 189 (100%), 170, 153, 139, and 127.
Step 1(d)xe2x80x94Preparation of 1,2-Difluoro-3-(2,2-difluorooctyl)benzene
Hydrogen fluoride-pyridine (70%) (25.2 ml) was added dropwise via a polypropylene syringe fitted with polythene tubing to a rapidly stirred suspension of 1,3-dibromo-5,5-dimethylhydantoin (14.2 g, 49.8 mmol) in dry dichloromethane (150 ml) at xe2x88x9270xc2x0 C. under dry nitrogen. A solution of the dithiolane of step 1(c) (14.5 g, 45.9 mmol) in dry dichloromethane (150 ml) was added dropwise and the reaction mixture was allowed to slowly warm (cooling bath fitted) to xe2x88x9210xc2x0 C. The brown homogenous solution was cooled to xe2x88x9270xc2x0 C. and the mixture was poured quickly into rapidly stirred mixture of basic alumina in dichloromethane cooled with a CO2 (solid)-acetone bath. After warming to ambient the mixture was filtered; the solvent was removed in vacuo and the residue was purified by column chromatography (light petroleum) to give a colourless liquid. Kugelrohr distillation (125xc2x0 C., 0.1 mm Hg) yielded the pure gem-difluoro compound (6.5 g, 54%); vmax 2980, 2965, 2860, 1625, 1595, 1490 s, 1380, 1285, 1270, 1210, 1035, 875, 825, 770, and 740 cmxe2x88x921, xcex4H 0.89 (3 H, t, Me), 1.22-1.39 (6 H, m, CH2), 1.51 (2 H, quint, CH2CH2C), 1.71-1.90 (2 H, m, CH2CH2C), 3.22 (2 H, td, JHF vic 16 and J1.5 Hz, CH2Ar), and 6.99-7.15 (3 H, m, ArH); m/z 262 (M+), 187, 176, 172, 165, 151, 141, 135, and 127.
Step 1(e)xe2x80x94Preparation of 2,3-Difluoro-4-(2,2-difluorooctyl)phenylboronic acid
2.5 M n-Butyllithium (8.3 ml, 21 mmol), was added dropwise to a stirred solution of the gem-difluoro compound of step 1(d) (5.41 g, 20.6 mmol) in dry THF (70 ml) at xe2x88x9270xc2x0 C. under an atmosphere of dry nitrogen at such a rate that the temperature did not rise above xe2x88x9260xc2x0 C. The temperature was maintained for 2 h and trimethyl borate (4.7 ml, 41 mmol) was added dropwise. The mixture was allowed to warm to ambient temperature overnight and 10% hydrochloric acid was added. After stirring for 15 min the mixture was extracted with ether (twice) and the combined extracts were dried and the solvent was removed in vacuo to give the required boronic acid compound in the form of a creamy solid (5.59 g) which was used without further purification.
Step 1(f)xe2x80x94Preparation of 4xe2x80x2-Bromo-2,3-difluoro-4-(2,2-difluorooctyl)biphenyl
To a degassed mixture of 1-bromo-4-iodobenzene (4.84 g, 17.1 mmol), 1,2-dimethoxyethane (50 ml), and 2 M aqueous sodium carbonate (50 ml) was added tetrakis (triphenylphosphine) palladium (0.593 g, 0.513) mmol) under dry nitrogen. The mixture was heated under gentle reflux with rapid stirring and a solution of the boronic acid compound of step 1(e) (5.24 g, 17.1 mmol) in THF (10 ml) was added dropwise and heated under reflux for 5 h. Water was added and the mixture was extracted with ether (twice) and dried. The solvent was removed in vacuo and the crude product was purified by column chromatography (n-hexane) to give a the required biphenyl compound in the form of a white solid (2.06 g, 29%); vmax 2950, 2930, 2870, 2860, 1590 w, 1480, 1465 s, 1390, 1220, 1190, 1130, 1100, 1030, 1010, 895, 840, and 800 cmxe2x88x921, xcex4H (400 MHz) 0.88 (3 H, t, Me), 1.23-1.38 (6 H, m, CH2), 1.53 (2 H, quint, CH2CH2C), 1.78-1.93 (2 H, m, CH2CH2C), 3.24 (2 H, td, JHF vic. 16 and J1 Hz, CH2Ar), 7.12 (1 H, t, J8 Hz, 5- or 6-H), 7.14 (1 H, t, J8 Hz, 5- or 6-H), 7.41 (2 H, dd, J8 and 1.5 Hz, 2xe2x80x2- and 6xe2x80x2-H), 7.59 (2 H, d, J8 Hz, 3xe2x80x2- and 5xe2x80x2-H); m/z 418 (M+), 416 (M+), 399, 332, 299, 285 (100%), 283 (100%), 268, 252, 232, and 210.
Step 1(g)xe2x80x94Preparation of 4xe2x80x3-Decyloxy-2,3-difluoro-4-(2,2-difluorooctyl)-1,1xe2x80x2:4xe2x80x2,1xe2x80x3-terphenyl (Compound 13)
Quantities: bromobiphenyl 7 (0.83 g, 1.94 mmol), 2-(4-decyloxyphenyl)-[1,3,2] dioxaborinane (0.95 g, 2.98 mmol), 1,2-dimethoxyethane (30 ml), 2 M aqueous sodium carbonate (30 ml), tetrakis(triphenyl-phosphine) palladium (67 mg, 0.058 mmol). The experimental procedure was as described for the preparation of the biphenyl compound of step 1(f). The crude product was purified by column chromatography (10% dichloromethane in light petroleum) to give the Compound 13 (0.78 g, 70%) (from ethanol-ethyl acetate); transitions (xc2x0 C.) C 98.9 SmC 133.5 I; vmax 2950, 2920, 2850, 1600, 1500, 1485, 1460 s, 1395, 1285, 1250, 1180, 1130, 1100, 1030, 895, 820, and 800 cmxe2x88x921, xcex4H 0.89 (6 H, overlapping t, 2 x Me), 1.23-1.41 (18 H, m, CH2), 1.23-1.41 (4 H, quint, CH2), 1.75-1.95 (4 H, m, CH2), 3.25 (2 H, br t, CH2Ar), 4.01 (2 H, t, OCH2), 6.99 (2 H, d, J8 Hz, 3xe2x80x3- and 5xe2x80x3-H), 7.14 (1 H, br t, J7 Hz, 5-H), 7.21 (1 H, td, J7 and 1.5 Hz, 6-H), 7.57 (2 H, d, J8 Hz, 2xe2x80x3- and 6xe2x80x3-H), 7.63 (2 H, d, J8 Hz, ArH), and 7.65 (2 H, d, J8 Hz, ArH); m/z 570 (M+), 550, 480, 456, 443, 430 (100%), 413, 401, 387, 372 and 295.
In order to reduce the lateral dipole and hence the melting point of the materials, a trifluoro-substituted intermediate 2.5 was prepared starting from compound 2.1 using steps 2(a) to 2(d) in the reaction scheme below in a similar manner to that used in Example 1 to prepare the analogous 1,2-difluorophenyl intermediate. Intermediate 2.5 was then involved in palladium-catalysed cross-coupling reactions with boronic acids 2.6 and 2.8 to generate a monofluorobiphenyl (2.7) and a monofluoroterphenyl (2.9). 
Reagents
(a) . . . (i) n-BuLi; (ii) 1,2-epoxyoctane; (iii) BF3.Et2O, xe2x88x9270 to xe2x88x9230xc2x0 C.
(b) . . . chromic acid, ether
(c) . . . ethane-1,2-dithiol, BF3.AcOH
(d) . . . HF-pyridine, dibromodimethylhydantoin, CH2Cl2, xe2x88x9270 to xe2x88x9210xc2x0 C.
(e1/e2) . . . 1,2-dimethoxyethane, Pd(PPh3)4, 2M Na2CO3 
In order to produce compounds containing the (CH2CF2CH2 CF2R) unit, a novel route (see the reaction scheme below) was devised. The xcex2-diketone (3.6) is considered to be suitable as a intermediate in the synthesis of materials according to the present invention with a tetrafluorinated alkyl chain. 
Reagents
a . . . (i) NaH, dioxan; (ii) CuBr
b . . . (i) 2M NaOH, EtOH; (ii) HCl, 80xc2x0 C.; (iii) EtOH, conc. H2SO4. reflux
c . . . NaH, THF 
Reagents
a . . . (i) NaH, dioxan; (ii) CuBr
b . . . (i) 2M NaOH, EtOH; (ii) HCl, 80xc2x0 C.; (iii) EtOH, conc. H2SO4. reflux
c . . . NaH, THF
Compound 4.5 containing a decyloxy chain was prepared according to the reaction scheme below, and compounds 4.6 to 4.10 were prepared by analogous methods. 
Reagents
a . . . 1,2-dimethoxyethane, 2M Na2CO3, Pd(PPh3)4 
Signs of photo-sensitivity were observed for compound 4.5 with the formation of a greenish colour on the portion of sample exposed to sunlight. Compounds 4.6-4.10 did not exhibit any photo-sensitivity.
A similar sequence to that used in Example 4 above was used to prepare the trifluoroterphenyl compound 5.15. The optical microscopy shows a highly birefringent schlieren texture with many multi-brush (six or more) defects. There are also, what appears to be, two brush defects. 
Reagents
a . . . 1,2-dimethoxyethane, 2M Na2CO3, Pd(PPh3)4 
A xcex2-monofluoroalkyldifluorophenylpyrimidine compound 6.3 was prepared according to the reaction scheme below 
Reagents
a . . . (i) LDA, THF, xe2x88x9290xc2x0 C.; (ii) 1,2-epoxyoctane; (iii) BF3.Et2O
b . . . DAST. Dichloromethane
present invention having a chiral site as a chiral dopant as well as being an additive for enhancing the tranverse dipole moment of a liquid crystal composition.
The synthetic scheme below was used to prepare the xcex1,xcex1-difluoro compound 7.9 which exhibits a higher melting point and clearing point than the analogous xcex2-compound There is also a lowering of SmCx stability and the introduction of a 23xc2x0 C. SmA phase. The orthogonal phase was never observed for any of the xcex2-fluoro-compounds prepared. The optical texture is more typical SmC schlieren, but again the two brush defects are quite distinct and indicative of alternating-tilt layers. An alkyl-substituted example 7.10 was also prepared in an analogous way 
Reagents
a . . . (i) n-BuLi; (ii) n-hexanal
b . . . chromic acid, ether
c . . . 1,2-ethanedithiol, BF3.Et2O
d . . . HF-pyridine, dichloromethane, xe2x88x9270xc2x0 C.
e . . . (i) n-BuLi; (ii) B(OMe)3; (iii) HCl
f . . . 1-bromo-4-iodobenzene, 1,2-dimethoxyethane, 2M Na2CO3, Pd(PPh3)4 
g . . . tert-butyl methyl ether, Pd(PPh3)4, 2M Na2CO3 
The reaction scheme below was used to prepare an ether-linked fluorinated chain compound 8.4:
Reagents
a . . . tert-butyl methyl ether, Pd(PPh3)4, 2M Na2CO3 
b . . . (i) Pd/C, ethyl acetate; (ii) (R)-2-fluorooctanol, DEAD, PPh3. THF
The improved transverse dipole moments which are achievable by compounds of the present invention will be apparent from the list below:
(The dipole moments were measured following the procedure of E. P. Raynes (1984) Mol. Cryst. Liq. Cryst. Lett., v1 p 69)
It has been shown that adding a compound of the invention such as 
into a SMC host material, such as that comprising a 1:1:1:1 mixture of compounds H1 to H4 below, retains good phase transitions and that the compound is miscible across the phase diagram: 
I 119.1-118.8 N 110.7 SmA 99.5 SmC 18.9 K (Mpt=30.2xc2x0 C.)
The present invention will now be described in further detail and with reference to the accompanying drawing which is a schematic section through an electro-optical liquid crystal device according to the present invention.